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Commitd70cec8

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MiaoheLintorvalds
authored andcommitted
mm: mmap: merge vma after call_mmap() if possible
The vm_flags may be changed after call_mmap() because drivers may set someflags for their own purpose. As a result, we failed to merge the adjacentvma due to the different vm_flags as userspace can't pass in the same one.Try to merge vma after call_mmap() to fix this issue.Signed-off-by: Hongxiang Lou <louhongxiang@huawei.com>Signed-off-by: Miaohe Lin <linmiaohe@huawei.com>Signed-off-by: Andrew Morton <akpm@linux-foundation.org>Reviewed-by: Andrew Morton <akpm@linux-foundation.org>Link:http://lkml.kernel.org/r/1594954065-23733-1-git-send-email-linmiaohe@huawei.comSigned-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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‎mm/mmap.c‎

Lines changed: 21 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -1690,7 +1690,7 @@ unsigned long mmap_region(struct file *file, unsigned long addr,
16901690
structlist_head*uf)
16911691
{
16921692
structmm_struct*mm=current->mm;
1693-
structvm_area_struct*vma,*prev;
1693+
structvm_area_struct*vma,*prev,*merge;
16941694
interror;
16951695
structrb_node**rb_link,*rb_parent;
16961696
unsigned longcharged=0;
@@ -1774,6 +1774,25 @@ unsigned long mmap_region(struct file *file, unsigned long addr,
17741774
if (error)
17751775
gotounmap_and_free_vma;
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1777+
/* If vm_flags changed after call_mmap(), we should try merge vma again
1778+
* as we may succeed this time.
1779+
*/
1780+
if (unlikely(vm_flags!=vma->vm_flags&&prev)) {
1781+
merge=vma_merge(mm,prev,vma->vm_start,vma->vm_end,vma->vm_flags,
1782+
NULL,vma->vm_file,vma->vm_pgoff,NULL,NULL_VM_UFFD_CTX);
1783+
if (merge) {
1784+
fput(file);
1785+
vm_area_free(vma);
1786+
vma=merge;
1787+
/* Update vm_flags and possible addr to pick up the change. We don't
1788+
* warn here if addr changed as the vma is not linked by vma_link().
1789+
*/
1790+
addr=vma->vm_start;
1791+
vm_flags=vma->vm_flags;
1792+
gotounmap_writable;
1793+
}
1794+
}
1795+
17771796
/* Can addr have changed??
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*
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* Answer: Yes, several device drivers can do it in their
@@ -1796,6 +1815,7 @@ unsigned long mmap_region(struct file *file, unsigned long addr,
17961815
vma_link(mm,vma,prev,rb_link,rb_parent);
17971816
/* Once vma denies write, undo our temporary denial count */
17981817
if (file) {
1818+
unmap_writable:
17991819
if (vm_flags&VM_SHARED)
18001820
mapping_unmap_writable(file->f_mapping);
18011821
if (vm_flags&VM_DENYWRITE)

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